116 The president's address. 



think all who are competent to judge will discern that, whatever 

 its use might have been, it could have been of but slight utility in 

 enabling its possessor to amplify small objects. Sir David Brewster, 

 to whom Mr. Layard submitted it, thus describes it: — " This lens 

 is plano-convex, and of a slightly oval form, its length is 1-^ 

 inches, and its breadth, 1*-$ inches; it is about ^ of an inch 

 thick, and a little thicker at one side than the other ; its plane 

 surface is pretty even, though ill-polished and scratched ; its convex 

 surface has not been ground or polished on a spherical concave 

 disc, but has been fashioned on a lapidary's wheel, or by some 

 method equally rude. The convex side is tolerably well polished, 

 and though uneven, from the mode in which it has been ground, it 

 gives a tolerably distinct focus at 4^- inches distance from the plane 

 side. It is obvious from the shape and rude cutting of the lens 

 that it could not have been intended as an ornament ; we are 

 entitled, therefore, to consider it as intended to be used as a lens, 

 either for magnifying or for concentrating the rays of the sun, 

 which it does however very imperfectly." 



This lens was found in the Royal Palace of Nimroud, buried 

 beneath a heap of fragments of blue, opaque glass (?) apparently the 

 enamel of some object in ivory or wood, bat it was honoured by 

 being in the same room as the royal throne, and may now be seen 

 by any one interested in this subject in the Assyrian collection at 

 the British Museum, in a glass table case, supported in an upright 

 position by wire standards. We may probably date the construc- 

 tion of this lens back to the time of Ninus and his wife Semiramis, 

 for it was only in their reign that much encouragement was given 

 to the arts, and that period would be about 2,000 years before the 

 Christian era ; thus entitling it to be considered the oldest lens 

 extant, if lens it be. It is not of glass but of rock crystal. 



Passing from this digression, we arrive at the early part of the 

 13th century, where we find Friar Roger Bacon hard at work in 

 his laboratory at Oxford, applying his mathematical attainments 

 to the construction of such lenses as were suitable for improving 

 the sight, or, if not actually constructing them, laying down such 

 rules for doing so as to prove that he was sufficiently master of the 

 laws of refraction to be able to calculate the foci of segments of 

 spheres, and thus aiding their adaptation to the construction of 

 spectacles ; but even in these comparatively modern times we are 

 met by much obscurity in the history of lenses, some writers deny- 



